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Anti-interference enhancement related to pull-up resistor in single chip microcomputer

Published time:2016/10/17    Visitors:50次
Thermistors in electronic circuit design, the presence of interference so that designers are miserable, interference will lead to circuit abnormalities, and even lead to the final product can not be used properly. How to reduce or even avoid interference skillfully is always the key designers concerned, the anti-interference design of single-chip microcomputer is the more important one ring, this paper will introduce the anti-jamming and pull resistance of scm.
In order to realize the single chip microcomputer interference, first of all, we should consider the input impedance of each I/O port, the acquisition rate and other factors to design the peripheral circuit of the I/O port. Generally, the input impedance of a I/O port is determined by 3 conditions.
The first case: the I/O port has a pull-up resistor, and the pull-up resistor is the input impedance of the I/O port. Most people use 4K-20K resistors to do pull-up (PIC B with an internal pull-up resistor of about 20K).
Since the interference signal follows Ohm's law, it is less likely to choose a pull-up resistor in the presence of interference because the voltage generated by the interfering signal is less.
As the pull-up resistor is smaller, the more power consumption, so in household design, the pull-up resistor is generally 10-20K, and in the case of strong interference, pulling resistance can even be reduced to 1K. (if you want to abandon the pull on B port on a strong interference occasion, you must use an external pull-up.)
The second type: I/O port and other digital circuit output pin, at this point, I/O port input impedance is digital circuit output impedance, usually tens to hundreds of europe.
It can be seen that the use of digital circuit as an intermediary can reduce the impedance to the most ideal, in many industrial control panels can see a large number of digital circuits, in order to ensure the performance and protection of MCU.
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The third type: I/O port in parallel with a small capacitor.
Because the capacitor is ac - blocking DC, and the interference signal is instantaneous and instantaneous, the capacitor can filter the interference signal. But the cost is to reduce the rate at which I/O signals are collected, for example, on the serial port and the capacitor is not desirable because the capacitor filters out the digital signal as an interfering signal.
For some special devices, such as detection switch, Holzer element, and is capable of capacitor design, this is mainly because the switch quantity change is relatively slow, and can not form a very high rate, so even if the circuit of shunt capacitor, has no effect on the signal acquisition is not. This article mainly for the pull-up resistor on how to avoid the interference of SCM introduced, interference by the microcontroller is disturbed friends may wish to spend a few minutes reading, I believe there will be gains.
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